The invention relates to a charging device for a motor vehicle, wherein the motor vehicle is provided with an electric energy storage device, a DC-DC converter as well as a first hard-wired interface to a first external AC network for charging the electric energy storage device.
The basis of vehicle concepts that both conserve resources and are also climate and environmentally friendly is the electrification of the drive in modern motor vehicles in the form of hybrid and electric vehicles. The main component of an electrified drive train is a high capacity electric energy storage device. Based on the current development, secondary batteries in lithium ion technology at a voltage level in the high voltage range are available for such an electric energy storage device. In the case of plug-in hybrid vehicles, which are also called socket hybrid vehicles, and in the case of solely electric vehicles, the electric energy storage device is charged not only with the electric power generated in the vehicle, but also with electric power from external sources. The external charging can be carried out conductively or inductively. In the case of the conductive charging technology, the electric charging power is transferred in a hard-wired fashion through a conductor line. In the case of the inductive charging technology, the charging power is transferred by means of electromagnetic induction while the vehicle is moving.
When designing the architecture of the automotive electrical system, the external charging infrastructure has to be taken into consideration. This requirement is apparent from the prior art. EP 0 116 925 A2 describes an on-board battery charging device, in order to charge the battery of an electric vehicle from an external AC network while the vehicle is in a stationary mode. EP 0 610 258 B1 explains a schematic architecture of the automotive electrical system for charging the battery of an electric vehicle at a DC charging station. The principle of inductive charging of a battery of an electric vehicle while the vehicle is moving is described in U.S. Pat. No. 5,311,973 A.
The object of the present invention is to provide an improved charging device for an electric energy storage device in a motor vehicle.
This and other objects are achieved by a charging device for an electric energy storage device in a motor vehicle equipped with a DC-DC converter as well as a first hard-wired interface to a first external AC network for charging the electric energy storage device. The charging device has a second inductive interface to a second external AC network for charging the electric energy storage device of the vehicle. The output power of the DC-DC converter is used as the charging power of the electric energy storage device; and the input of the DC-DC converter can be supplied with electric power over the first and second interface.
It is a particular advantage of the present invention that the electric energy storage device can be charged over the first interface and/or the second interface when the motor vehicle is in the stationary mode. The first interface and the second interface have a common connection to the DC-DC converter for a simultaneous charging operation. The electric energy storage device can also be charged in the stationary mode, if only the first external AC network (hereinafter referred to as the AC charging) or only the second external AC network (hereinafter referred to as inductive charging) is available.
Such an approach offers the particular advantage of a cost effective architecture of the automotive electrical system having only one DC-DC converter that adjusts the charging voltage at the energy storage device. The electric power is fed to the power input of the DC-DC converter in three charging modes (AC charging, inductive charging, simultaneous AC and inductive charging).
Furthermore, there is an additional advantage of the invention in drive mode. The charging device allows the battery to be charged even when the vehicle is running. In this case, the energy storage device of the vehicle is charged over the second interface, i.e. the inductive interface, because a power transfer via electromagnetic induction takes place even while the vehicle is moving.
According to a preferred embodiment of the invention, the charging device has a third hard-wired interface to an external direct voltage source for charging the electric energy storage device. The input of the DC-DC converter can be supplied with electric power over the third interface.
Within the framework of this embodiment, additional charging modes can be implemented with the DC-DC converter located upstream of the secondary battery. When the vehicle is in the stationary mode, this configuration of the charging device allows the energy storage device to be charged over the third interface at a direct voltage source, such as a DC charging station or a DC station (hereinafter referred to as DC charging).
With the charging device, a DC charging operation can be simultaneously combined with an AC charging operation. An additional combination consists of DC charging with simultaneous inductive charging. The DC charging can also be conducted simultaneously with AC charging and inductive charging, so that the DC-DC converter is provided with electric power simultaneously over the first, second and third interfaces for charging the battery.
According to a further development of the invention, the DC-DC converter of the charging device is configured such that the lower limit of the nominal range of the input power of the DC-DC converter corresponds to at least the power that constitutes the lowest power from the set of the three maximum power outputs of the three interfaces. The configuration of the upper limit of the nominal range of the input power of the DC-DC converter corresponds at most to the sum of the maximum power outputs of the three interfaces.
Each of the three interfaces can be used to make available a maximum value of electric power to the DC-DC converter for charging the battery. This value is called the maximum output power of the interface. Each interface from the set of the three interfaces with the smallest maximum output power (or the smallest output power that is typically available during a charging operation, in the event of a deviation from the maximum output power) is relevant for the configuration of the DC-DC converter, because the value of this smallest maximum output power (or the smallest output power that is typically available) does not drop below the lower limit of the nominal range of the input power of the DC-DC converter. The configuration of the DC-DC converter according to this embodiment has the advantage that the charging device enables an energy efficient charging and the fastest possible charging of the energy storage device, if the charging is done separately over one of the three interfaces. Independently of which of the three interfaces is affected, the DC-DC converter works at an optimal operating point, which means with optimal efficiency. An optimal operating point is characterized by the fact that it lies within the nominal range of the input power of the DC-DC converter. In the event that the external charging infrastructure provides such a small amount of electric power or that the electric energy storage device has such a small charge acceptance that, during a separate charging operation over a single interface, a smaller amount of power than the maximum output power of this interface is fed to the DC-DC converter, then it may be quite likely that the DC-DC converter is working at an input power that is below its nominal range on the input side. However, this operating point is also in the operating range of the DC-DC converter, because the operating range of a DC-DC converter includes the power range below the nominal range.
The upper limit of the nominal range of the input power of the DC-DC converter corresponds, according to this embodiment, at most to the sum of the three maximum power outputs. If the upper limit of the nominal range of the input power of the DC-DC converter corresponds exactly to the sum of the three maximum power outputs, then it is ensured that the DC-DC converter is working at an optimal operating point, if the energy storage device is being charged simultaneously over all three interfaces, and the respective maximum output power is fed to the DC-DC converter over each of the three interfaces.
Preferably, the charging device is configured such that the electric energy storage device is designed for a maximum charging voltage of at most 1,000 volts. The first interface is designed for an effective value of the first external alternating voltage of at most 500 volts. The second interface is designed for a maximum induced voltage of at most 3,000 volts; and the third interface is designed for a maximum voltage of the external direct voltage source of at most 1,000 volts.
This embodiment has a special advantage. The charging device can be coupled via the first and the second interface with the most widely installed AC networks in the world (in particular, 1 phase grid systems at 50/60 Hertz up to 240 volts and 3 phase grid systems at 50/60 Hertz up to 480 volts) for charging the energy storage device. With respect to the electrical configuration, the charging device can be coupled via the third interface to both regulated and unregulated DC charging stations and/or also DC power grids and also directly to electric energy storage devices. This specific embodiment guarantees that the charging device exhibits a high compatibility with the external charging infrastructure that will most likely be available to the vehicle user and, as a result, ensures a high degree of charging efficiency. Not only the charging efficiency is included in the concept of charging efficiency, but also the charging power. A high charging efficiency at high charging power is reflected in a short charge time in order to load a defined amount of charge into the energy storage device. In this case a short charge time, i.e. a high charging efficiency, is extremely advantageous.
The invention is based on the considerations presented as follows.
The charging of the electric storage device in plug-in hybrids or electric vehicles is conventionally carried out conductively, i.e. hard-wired. To facilitate the charging operation for the customer, there is a move to develop methods for wireless energy transfer. This charging technique is referred to as inductive charging and is based on the fact that energy is transferred through a coil, which is embedded in the ground, to a second coil, which is mounted on the vehicle, by electromagnetic induction, for example.
In the case of conductive charging at an alternating current source, for example, at the standard home power mains connection, the charging current is rectified in the vehicle. The voltage is adapted to the charging voltage of the electric energy storage device. For this purpose an inter-vehicle charging device, which is constructed as an AC-DC converter, is used. The charging device consists, in highly simplified terms, of two components: a rectifier and a DC-DC converter.
Conductive charging can also take place at an external direct current source, for example, at a charging station. A DC-DC converter for voltage matching has to be provided in order to optimally charge the storage device.
In the case of inductive charging, a high frequency alternating voltage is generated at the coil in the vehicle. This high frequency alternating voltage is rectified near the coil, in order to reduce the electromagnetic radiation. Then, the voltage is changed, as a function of the inputs from the battery control unit, in a DC-DC converter.
In order to install together the conductive AC charging technique, the conductive DC charging technique and the inductive charging technique, a number of components are required, in addition to the respective systems for connecting components in the vehicle's electrical system. In over-simplified terms these components are an AC-DC converter with a DC-DC converter for the conductive AC charging technique, a DC-DC converter for the conductive DC charging technique and a coil with a rectifier and a DC-DC converter for the inductive charging technique. In particular, the three converters incur a high cost and require geometric installation space.
It is possible to achieve a significant simplification of the topology of the necessary electrical system of the vehicle and an effective cost-cutting by designing and dimensioning the DC-DC converter, which is used in the charging device for charging with the conductive AC charging technique, in such a way that the voltage conversion in the branch for the conductive DC charging technique and the voltage conversion in the branch for the inductive DC charging technique is also taken over at the same input of the DC-DC converter. The technical improvement of the DC-DC converter in the charging device is offset by the reduction of two additional DC-DC converters, a feature that is reflected in both a cost benefit and installation space advantage. In addition, a simplified cable harness can be used.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of a preferred embodiment when considered in conjunction with the accompanying drawing.